Method of replacing branch mains

ABSTRACT

A method is provided for replacing a length of a branch gas main 1 joined to a spine main 2 with a length of replacement main 7 having an outer diameter smaller than the inner diameter of the branch main. In the method access is gained to the bore of the branch main and one end of the replacement main 7 is fed along the branch main 1 via the access point and towards the spine main 2 until the branch main 1 has been replaced. During and after the feeding step gas is prevented from entering any clearance 20 between the mains 1 and 7 by means of a head 9 attached to the leading end of the main 7. After the feeding step a sealant 25 is injected into the branch main 1 to form a seal within the clearance 20.

This is a division, of application Ser. No. 07/786,784, filed on Nov. 1,1991, now abandoned.

The present invention relates to replacing an existing main with areplacement main.

Gas, water and sewage mains may need to be replaced when they developleaks or for other reasons. Leaks may develop at joints as a result ofleak paths appearing within the joints in the case of cast iron gasmains or as a result of cracks in the wall due to corrosion ormechanical damage in cast iron and other materials e.g. ductile iron andsteel, cement, brickwork or plastics.

In the case where the main to be replaced is a branch main joined to afluid-carrying spine main, present techniques of mains replacementnecessitate an excavation being made at the junction between the branchmain and the spine main to gain access thereto. This is frequently inthe middle of a busy thoroughfare and the excavation may lead todisruption of both pedestrians and traffic.

It is an object of the present invention to provide a method by which anexisting main can be replaced by a replacement main in such a way thatsuch disruption can be minimised.

According to an aspect of the present invention we provide a method forreplacing a branch main lying between and adjoining two fluid carryingspine mains with a replacement main having an outer wall with a smallerdiameter than the diameter of the inner wall of the branch main, themethod comprising gaining access to the bore of the branch main at apoint lying between the spine mains so that a first length of branchmain is formed between a first spine main and the access point and asecond length of branch main is formed between a second spine main andthe access point, feeding one end of a first length of replacement maininto the first length of branch main by way of the access point untilthe first length of branch main has been replaced, feeding one end of asecond length of replacement main into the second length of branch mainby way of the access point until the second length of branch main hasbeen replaced and then joining the other ends of the lengths ofreplacement main together.

Embodiments of the invention will now be described by way of exampleonly with reference to the accompanying drawings, in which:

FIG. 1 shows a length of a sub-ground branch main joined to a sub-groundspine feeder main carrying fluid, in this case gas,

FIGS. 2 to 6 show the steps in a first embodiment of a method for thereplacement of the branch main with a length of replacement main,

FIGS. 7 to 11 show the steps in a second embodiment of a method for thereplacement of the branch main,

FIG. 12 is an amplified longitudinally sectioned view of FIG. 9,

FIG. 13 is an amplified longitudinally sectioned view of FIG. 11, and

FIGS. 14 to 16 show the final three steps of a method for replacing abranch main lying between two spine feeder mains which are adjoined bythe branch main.

Referring to the drawings, FIG. 1 shows a length of branch main 1 joinedto a spine main of the same or larger diameter 2 both of which mains arelocated underneath the ground. The spine main 1 may be carrying gas,water or sewage although the invention is particularly suitable for thereplacement of gas-carrying mains. In FIG. 1 the spine main 2 is adistrict feeder main, the branch main 1 leading off therefrom andterminating in a closed end 3. In FIGS. 14 to 16 however, the branchmain 1 is also fed from a further spine main (not shown) at the otherend of the branch main 1. The steps shown in FIGS. 2 to 11 and describedin relationship thereto apply to the branch main 1 shown in FIG. 1.

In the first step of each embodiment of the method (FIG. 1) thespine-main distal end 3 of the branch main 1 is exposed by excavation,this end being remote from the spine main 2. Alternatively, anexcavation can be made between the spine main and distal end 3 to anyconvenient point, as required.

In the first version of the method (FIG. 2) a part 4 of the branch mainI is exposed at a convenient point which in this case is close to theend 3 and is sealed off from the flow of gas by the known technique of"bagging off". Here a pair of removable inflatable rubber bags 5, 6respectively are inserted into the main 1 at spaced apart positions andare inflated as shown temporarily to block the bore of the main 1.

In the next step of this method (FIG. 3) the end 3 of the main 1 isremoved by sawing or other well known technique to provide an accesspoint for the replacement main 7 to the bore of the branch main 1. Afull bore known-type gate valve or damper plate 8 is then connected asshown to the now open end of the branch main 1 and with the valve 8closed the bags 5 and 6 are deflated and removed through their insertionholes which are plugged or sealed as conventional. A length ofreplacement main 7 of length sufficient to line or replace the entirelength of the branch main 1 from its junction with the spine main 2 toits end 3 is selected, the main 7 being of a suitable syntheticmaterial, preferably polyethylene. The main 7 may comprise discretelengths fused together or a coil of such material. The outer diameter ofthe main 7 is smaller than the inner diameter of the branch main 2 topermit the replacement main 7 to be inserted into and fed along thebranch main 1.

As shown in FIG. 3 the replacement main 7 terminates at its leading endin a head 9 which in effect forms an integral part of the main 7. Thehead 9 may also be of a suitable synthetic resin material e.g.polyethylene in the form of a moulding and comprises a tubular body witha through-going bore, a rear portion 10 for connection to the end of thereplacement main and a front portion 11 having at least one and here twoannular vanes 12 and 13 spaced apart along and disposed around the outerwall of the head 9. While a head having two vanes is described there maybe more than two if desired or necessary. In use of the head 9, thevanes 12 and 13 form a close or tight fit with the inner wall 14 of thebranch main 1 so as to provide a gas-tight barrier to the flow of gasalong any clearance between the inner wall 14 of the branch main 1 andthe outer wall 15 of the replacement main 7 when the latter is insertedinto and pushed along the branch main 1. The external diameter of thevanes may be equal to or greater than the internal diameter of theexisting main to achieve the close or tight fit. The head 9 may beattached to the replacement main 7 in any convenient fashion for exampleby fusion, adhesive or as a force fit within the end of the main 7.Before however the head 9 is attached to the leading end of the main 7,this end is inserted through a known-type gland box or pig trap 16 (FIG.3). The gland box 16 has an entry wall 17 formed of elastomericcomponents which form a hole through which the end of the replacementmain 7 may be inserted, the edge forming the hole providing a flexibleseal for the outer wall 15 of the main 7. Once the leading end of themain 7 has been inserted into the gland-box 16 and pushed clear of itsmouth 18, the head 9 can be attached to the leading end of the main 7.After this step the head 9 is pulled back into the gland-box 16 as shownin FIG. 3. The other end of the replacement main 7 is closed by a knowntype cap with fitted purge valve 19 (FIG. 3) to provide means by whichany air within the main 7 can be removed by purging as will be describedsubsequently.

Referring to FIG. 4, in the next stage of the method the gland-box 16 isconnected to the valve 8, the valve 8 is opened and the main 7 is pushedfrom the gland-box 16 into the branch main 1. Gas entering the branchmain 1 from the spine main 2 is forced to enter the replacement main 7because the vanes 12 and 13 prevent its entering any clearance 20between the outer wall 15 of the replacement main 7 and the inner wall14 of the branch main 1. Pushing of the main 7 towards the spine main 2can be effected by hand or mechanically by means of a conventional pipepusher machine.

The replacement main 7 is pushed along the branch main i until the head9 reaches and enters the spine main 2 (FIG. 5). The main 7 is thenretracted a short distance until the head 9 is securely located in thebranch main 1. This point can be determined by monitoring the pressurein the clearance 20 which will be positive when the head 8 is inside thespine main 2 but will drop to zero when the head 8 is once again insidethe branch main 1. Alternatively or in addition the head couldincorporate a TV camera or probes to detect the spine main 2.

The head 9 could be retracted still further if it is desired to replacea shorter section of branch main 1. The purge valve 19 is opened topermit gas to purge any air from the main 7 and then the valve 19 isclosed.

The gland-box 16 is then disconnected from the valve 8 and is slid alongthe main 7 towards the purge valve 19. Next, the valve 8 is disconnectedfrom the end 21 of the branch main I and this too is slid along the main7 towards the valve 19. Alternatively, both valve and gland box canremain joined and be slid along the main still connected and then bedisconnected from each other.

A so called "squeeze off" is then applied to the main 7 between the end21 of the branch main 1 and the valve 8 by means of a pair of known typesqueeze rolls 22 and 23 which squeeze the main 7 flat to prevent gasreaching the valve 19. With the squeeze off still applied the purgevalve 19 is removed.

Referring to FIG. 6 the gland box 16 and valve 8 are then slid off theend 24 of the main 7 with the squeeze off still applied and then the endof the replacement main 7 is closed by means of a cap 24 which may be ofa synthetic resin material e.g. polyethylene and which is fused oradhered to the main 7 in any suitable manner. The squeeze off is thenremoved. Finally a conventional sealant injection device (not shown) isfitted to the end 21 of the branch main 1 and the clearance 20 betweenthe branch main 1 and the replacement main 7 up to the head 9 is filledwith a suitable sealant 25 such as a cementitious grout, cement, epoxyor anaerobic sealant to provide a secondary gas-tight permanent seal inaddition to that formed by the vanes. An end cap seal device may benecessary to achieve a temporary seal between the outside of the main 7and the branch main 1 to allow the sealant to fully fill the gap.

In the method described with reference to FIGS. 2 to. 6, a fairly largequantity of sealant is required to fill the clearance 20 between thebranch main 1 and the replacement main 7 up to the head 9. While ingeneral it is desirable to fill this clearance, it is not absolutelyessential as long as an effective seal is formed somewhere in theclearance.

This is achieved by the method shown in FIGS. 7 to 11 and involves theuse of the modified head shown in detail in FIGS. 12 and 13. Unlessotherwise indicated, the components in FIGS. 7 to 13 are identical tothose shown in FIGS. 1 to 6 and therefore bear identical referencenumerals.

Referring to FIGS. 12 and 13, the head 9 is identical to that describedin FIGS. 3 to 6 except that extending through an aperture in the wall ofthe head 9 located between the vanes 12 and 13 is an injection nozzle 30which is force fitted or glued to the head 9. The inlet end 31 of thenozzle 30 terminates inside the bore of the head 9, while the outlet end32 of the nozzle 30 terminates between the vanes 12 and 13.

In use, with the head 9 positioned as shown within the branch main 1,there is formed between the inner wall 33 of the branch main 1, thevanes 12 and 13 and the outer wall 34 of the head 9 lying between thevanes 12 and 13, an annular chamber 35 in which the sealant may beinjected via the nozzle 30 as shown in FIG. 13. In this way a seal maybe formed with a relatively small amount of sealant.

In use, the sealant is supplied to the nozzle 30 by means of a flexiblee.g. polyethylene hose 36 which as shown in FIG. 12 is connected to theinlet end 31 of the nozzle 30. The hose 36 extends rearwardly throughthe head 9 and through and out of the far end of the replacement main aswill be described in more detail subsequently. The hose 36 is connectedto a pump (not shown) which pumps sealant along the hose 36 to thenozzle 30 where it is discharged into the annular chamber 35. When thischamber 35 is full as indicated by an increase in pumping pressure, thehose 36 may be removed from the nozzle 30 and then removed from thereplacement main. To this end the hose 36 is connected to the nozzle 30by a breakable-type connection whereby the hose 36 may simply be snappedoff from the nozzle 30 after the clearance has been filled with sealant.

As shown in FIG. 12, to prevent in use ingress of dirt and other debrisinto the head 9 during insertion into the branch main 1, the bore of thehead 9 may be temporarily blocked by a conventional inflatable rubberbladder 37 which can be positioned near the front end of the head 9 asshown. The bladder 37 is inflated (and deflated) by means of a hose 38which like the hose 36 extends rearwardly through the head 9 and throughand out of the far end of the replacement main as will be described inmore detail subsequently.

Referring to FIG. 7, this step of the second method is similar to thestage described in relation to FIG. 3 except that the head 9 is providedwith the bladder 37 which has been inflated before the head 9 isinserted into the gate valve 8. The bladder hose 38 extends rearwardlythrough the head 9, the replacement main 7 and a known type pipe gland39 to a source of compressed air (not shown). In addition of course thenozzle hose 36 also extends rearwardly through the head 9, thereplacement main 7 and the pipe gland 39 to a suitable sealant pump (notshown). The pipe gland 39 forms a seal between the replacement main 7and the hoses 36 and 38.

In FIG. 8, the main 7 has been pushed into the branch main 1 via thegland box 16 in a manner similar to that previously described inrelation to FIG. 4.

Referring to FIG. 9, the step here is similar to that previouslydescribed with reference to FIG. 5 except that as the bore of the head9, and therefore the replacement main 7, is blocked by the inflatedbladder 37 there is no need to squeeze off the main 7. At this stage, asealant of the type previously mentioned is pumped along the hose 36 toemerge into the annular chamber 35 and form a seal therein as shown inFIG. 10.

After the sealant has been allowed to set, the hose 36 is snapped offfrom the nozzle 30 and removed from the main 7 via the pipe gland 39.Then the bladder 37 is deflated and removed via its hose 38 through thepipe gland 39.

A squeeze off is then applied to the main 7 between the end 21 of thebranch main 1 and the purge valve 19 and with the squeeze off stillapplied the gland box 16, valve 8 and pipe gland 39 are slid off the end24 of the main 7 and then the end of the replacement main 7 is closed bymeans of a cap so that the position in FIG. 11 is reached.

The head 9 may be dispensed with if the replacement main 7 itself isfitted with the nozzle 30 and vanes 12 and 13. These could be fitted tothe main 7 at the factory where the main is produced and supplied to theuser complete with nozzle hose 38 connected to the nozzle 30.

Referring to FIGS. 14 to 16 where parts and components similar to thoseshown in FIGS. 1 to 13 bear similar reference numerals a branch main 50lies between two spine mains, only one 51 being shown, the main 50adjoining the spine mains at either end.

Previously to the stage shown in FIG. 14, a section of the branch main50 located at a point between the spine mains where traffic andpedestrian disturbance is minimal is removed by sawing or othertechnique to gain access to the bore of the branch main 50. At eitherside of the section before its removal bags similar to those shown inFIGS. 2 and 3 are inserted to temporarily block the bore of the main 50to each spine main. After removal of the section and in consequencethereof a first length 52 of branch main 50 is formed between the firstspine main 51 and the open end 53 of the length 52 and a second length54 of branch main 50 is formed between a second spine main (not shown)and the open end 55 of the length 54 as shown in FIG. 7.

Each of the lengths 52 and 54 of branch main may be replaced by suitablecorresponding lengths 56 and 57 of replacement mains of a materialsimilar to that previously described, each of the lengths 56 and 57having outer diameters smaller than the internal diameter of the branchmain 50. Any suitable replacement technique can be used for example theso-called "Blackburn process" described in published European patentapplication No. 0068657.

Preferably however, at least one of the lengths of branch main isreplaced by the technique shown in FIGS. 2 to 5 or FIGS. 7 to 13previously described.

In FIG. 14 both lengths of branch main have been replaced by thetechnique described in FIGS. 2 to 5. In the position shown in FIG. 14the corresponding purge valves, gland-boxes and valves have been removedfrom the lengths 56 and 57 after a squeeze off has been applied by therespective rolls 22 and 23, the ends of the lengths 56 and 57 lyingadjacent to each other and the ends being open.

Next with the squeeze off still applied (FIG. 15) the ends 58 and 59 ofthe lengths 56 and 57 are connected together by any convenient meanssuch as by butt-fusion or as shown in FIG. 15 by means of a known typeelectrofusion sleeve 60.

Finally (FIG. 16) the squeeze offs are removed. In this way gas or otherfluid can flow between the spine mains by way of the replacement mains.

The technique described in FIGS. 14 to 16 can be used with advantage toreplace any branch main which is too long to be replaced by a singlelength of main, the site for any necessary excavation being selected soas to provide a minimum of disruption to traffic and pedestrians.

We claim:
 1. A method for replacing a branch main lying between andadjoining two fluid carrying spine mains with a replacement main havingan outer wall with a smaller diameter than the diameter of the innerwall of the branch main, the method comprising gaining access to thebore of the branch main at a point lying between the spine mains so thata first length of branch main is formed between a first spine main andthe access point and a second length of branch main is formed between asecond spine main and the access point, feeding one end of a firstlength of replacement main into the first length of branch main by wayof the access point until the first length of branch main has beenreplaced, feeding one end of a second length of replacement main intothe second length of branch main by way of said access point until thesecond length of branch main has been replaced and then joining theother ends of the lengths of replacement main togetherwherein one end ofeach said length of replacement main has at least two spaced annularvanes disposed therearound and extended from an outer wall thereof todefine a clearance between the replacement main and the branch main whenthe replacement main has been fed into the branch main, and furthercomprising a step of injecting a substance capable of forming a sealinto said clearances, via an injection point in the wall of thereplacement main and located between said vanes.